Refactor Participable

There are several changes to this module:

1. The use of an explicit stack in Participable#participants
2. Proc behaviour has been changed
3. Batch permissions checking

== Explicit Stack

Participable#participants no longer uses recursion to process "self" and
all child objects, instead it uses an Array and processes objects in
breadth-first order. This allows us to for example create a single
Gitlab::ReferenceExtractor instance and pass this to any Procs. Re-using
a ReferenceExtractor removes the need for running potentially many SQL
queries every time a Proc is called on a new object.

== Proc Behaviour Changed

Previously a Proc in Participable was expected to return an Array of
User instances. This has been changed and instead it's now expected that
a Proc modifies the Gitlab::ReferenceExtractor passed to it. The return
value of the Proc is ignored.

== Permissions Checking

The method Participable#participants uses
Ability.users_that_can_read_project to check if the returned users have
access to the project of "self" _without_ running multiple SQL queries
for every user.

1 files changed, 1 insertions, 1 deletions

diff --git a/app/models/note.rb b/app/models/note.rb
index 55b98557244..35e5258fe3f 100644
--- a/app/models/note.rb
+++ b/app/models/note.rb
@@ -6,7 +6,7 @@ class Note < ActiveRecord::Base
 
   default_value_for :system, false
 
-  attr_mentionable :note, cache: true, pipeline: :note
+  attr_mentionable :note, pipeline: :note
   participant :author
 
   belongs_to :project